The present invention relates to an inflatable woven tubular belt.
Known from EP 1 056 894 B1 is an inflatable belt which is installed in a motor vehicle serving as a passenger air bag in case of a collision. DE 199 32 940 A1 shows a two-layer belt, particularly for a vehicular seat belt inflatable at least in part, the belt being formed as a flat tubular belt featuring a lower (first) layer (UWL) and an upper (second) layer (OL) wherein the lower layer (UWL) is woven and incorporating non-elastic warp threads (UK) and the upper layer (OL) is made in a material which is elastic lengthwise in the belt.
Further seat belt systems involving an air bag engineered as a tubular belt are known featuring two belt layers with a folded air bag woven fabric in-between. It is, of course, natural that such an engineered solution is more bulky as compared to a conventional “two-dimensional” seat belt, even when the belt is engineered with a low profile. Problems tend to occur with such belts particularly when negotiating deflector fittings for which a satisfactory solution is still wanted. When the belt is negotiating a deflector fitting or being rolled up on the retractor a movement occurs of the portion of the seat belt located far from the deflection or rolling axis relative to the portion of the belt nearer to the rolling or retraction axis resulting in trapping which produces creases to the detriment of the belt and adding to the discomfort of wearing the belt.
The solution as proposed in German Patent DE 199 32 940 A1 has also turned out to be non-optimal, it having been discovered that although the elastic warp threads in a layer are capable of compensating distortion when the belt is negotiating the fittings and when being retracted, the warp threads of both layers, i.e. the upper and lower layer need to be engineered for a minimum ultimate load to be fully functionable. In this case it is known that elastic warp threads have no appreciable ultimate load capacity.
This is why the object of the invention is to propose a belt which now avoids or at least diminishes the drawbacks known in prior art particularly as regards the distortion involved in negotiating the fittings and during retraction. This object is achieved by a belt in accordance with the invention, so that the number of first warp threads in the upper woven layer is approx. 1.5 times to three times greater than the number of first warp threads in the lower woven layer it is now achieved to advantage that the belt exhibits an optimum response on being rolled in and out of the retractor. Its response to negotiating the fittings is now also satisfactory. Thanks to the engineering in accordance with the invention the corrugations and “banana” curvatures in the belt as known in prior art after just short usage of the belt are now avoided. It has surprisingly been discovered that the woven layer having fewer warp threads than the other woven layer now tends to “guide” the other woven layer when negotiating a fitting, it adjusting to the contour of the other woven layer having more warp threads.
This object is also achieved by a belt in accordance with the invention, in this case so that the yarn count of first warp threads in the upper woven layer is approx. 1.5 times to three times greater than the yarn count of first warp threads in the lower woven layer it is now achieved to advantage that the belt exhibits the same response as previously set forth. In this description it is understood that the first warp threads and second warp threads differ by the first warp threads handling the tension in the belt in accordance with the invention when functioning as a seat belt, whilst the second warp threads—together with the weft threads—represent the tube-forming components which substantially handle no tensile force lengthwise in the tubular belt.